This invention relates to a hand-held device for the local heat treatment of the skin, in particular a facial skin portion, with the aid of an electrically heatable treatment surface which can be brought into contact with the skin.
It is well-known that the local application of heat to a portion of the skin, e.g. of the face of a patient leads to an active hyperemia with capillaroscopically detectable widening of the small vessels of the skin, especially of the superficial plexus, connected with a strong acceleration of local blood flow due to the release of acetyl choline.
This hyperemia affords:
(a) an increase of absorption. The acceleration of the velocity of blood flow is accompanied by an increase of the lymphatic flow. Thereby products of normal digestion and pathological secretions are more rapidly transported away from a diseased location. Moreover, substances brought into contact with the outer surface of the skin are more rapidly transported away, once they have reached the corium because the concentration gradient between the corium and the blood is larger in the hyperemic skin;
(b) an antibacterial effect;
(c) an improved feeding of the tissues; and finally
(d) an analgesic effect.
Transportation of a substance through the horny layer of the skin, which layer due to its barrier functions constitutes the main obstacle to the penetration of substances from the outside through the skin, increases with an increase of skin temperature. The increase of the permeability constant with increasing temperature is considerably greater than the increase of the said constant by hydration. There are two reasons for this effect, namely the increase of the activation energy of the molecules of a penetrating substance (increased molecular motion) and the softening of the lipids in the horny layer by increased temperature.
Known devices containing the initially described electrically heatable treatment surface for heat treating the skin as well as a thermostat for switching on and off an electrical heating element suffer from the drawback that the temperature of the treatment surface is subject to larger fluctuations in spite of the control of electrical heating. On the one hand, this cause a danger of overheating which can cause local burns in particular in sensitive parts of the face, when the temperature rises noticeably above 40.degree. C. On the other hand, there is the drawback of excessive cooling which means a loss of time before the device can again be used effectively, namely until the temperature of the treatment surface has risen again to the desired approximately 40.degree. C., a fact which must be determined, for instance, by touching the treatment surface with a finger. Moreover, the known devices are usually unwieldy and difficult to use on strongly curved portions of a patient's body.